Laterite Definition for Newbies

["Colin Anderson" <colin_d_anderson at hotmail_com>]

for those still interested..

while browsing through the dictionary of geological terms by bates and 
jackson I ran across the definition of laterite:

Laterite: A highly weathered red subsoil or material rich in secondary 
oxides of iron, aluminum, or both, nearly devoid of bases and primary 
silicates, and commonly with quartz and kaolinite.  It develops in a 
tropical or forested warm to temperate climate, and is a residual 
product of weathering.

So, what is kaolinite, and what effect might it have o laterite quality?

Kaolinite: a common clay mineral of the kaolin group.  It is the 
characteristic mineral of most kaolins, and is polymorphous with dickite 
and nacrite.  Kalinite is a high alumina  clay mineral that does not 
appreciably expand under varying water content and DOES NOT EXCHANGE 
IRON or magnesium.  

So what, I don't know, just excellent background for those of us less 
experienced with clays, probably of no value to the experts around.  

All I gather from this is that we can't depend on the kaolinite portion 
'often' found in laterites to deliver any iron exchange capability.  

Question:  What ions can Kaolinite colloids exchange?  Can iron be 
exchanged by Smectites or Illites?  Another question on clays and 
colloidal properties--Is cation exchange capacity really and effective 
and/or accepted term for emersed clays?  It seems to me that CEC is a 
term derived for the description of non-saturated soils.

Colin Anderson

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